The present invention relates to a spray dispenser, especially a hand-held spray can in which a spray is emitted upon manual actuation of a valve.
Hand-held spray dispensers are known in which a liquid product is contained within a flexible bag situated within a cylinder. Gas occupies a space between the bag and the cylinder. The gas, which has been pre-pressurized at the factory, functions to constantly compress the bag for expelling the contents whenever a discharge valve of the dispenser is depressed. In order to ensure that a sufficient amount of pressurized gas is available for discharging the entire liquid contents of the bag, a hydrocarbon-containing gas is usually employed. Such a gas is, however, generally realized as constituting an environmental pollutant.
Hand-held spray dispensers are also known in which a piston is housed within a container below a product to be dispensed, the product possibly being disposed within a flexible bag. By advancing the piston toward a valved end of the container, the bag is compressed to expel the product. Exemplary of such devices are the disclosures of U.S. Pat. Nos. 1,197,210; 2,728,097; 3,195,168; and 3,815,787. An advantage of a dispenser in which the product is pressurized by a mechanically-advanced piston is that no environmentally polluting gases are needed.
In the above-mentioned U.S. Pat. Nos. 1,197,210 and 3,815,787, the piston carries external screw threads which mate with internal screw threads of an outer sleeve. When the outer sleeve is rotated, the piston is longitudinally advanced to collapse a bag in which the product is carried. One shortcoming of such an arrangement is that liquid or solid products carried by the bag cannot be compressed to store energy. Hence, the piston must be advanced simultaneously with actuation of the valve in order to dispense the product.
It is conventional to use a multi-piece piston having a spring disposed between the pieces in order to store energy (see above-mentioned U.S. Pat. No. 3,195,168). However, a spring-biased piston does not always impart a continuously uniform pressure to the product, whereby the spray may not be uniform.
Another shortcoming of the arrangements disclosed in U.S. Pat. Nos. 1,197,210 and 3,815,787 involves the need to prevent rotation of the piston in order to ensure that the piston will advance longitudinally in response to rotation of the outer sleeve. In U.S. Pat. No. 3,815,787, that result is achieved by the provision of a stationary thin-walled cylinder having longitudinal guide slots into which radial lugs of the piston project. The thin-walled cylinder forms an inner wall of the bag-containing body, whereby there exists the possibility that the bag could become pinched between the guide slots and the piston and thus be ruptured as a consequence.
In U.S. Pat. No. 1,197,210 the piston is attached directly to the bag which means that the bag will tend to become twisted when resisting rotation of the piston unless the bag is formed of a relatively rigid material. Such material, however, will impede the collapsing of the bag, requiring that considerable force be applied to advance the piston.